The proposed research is part of a project whose long-term goal is to elucidate the role of mechanical properties of skin in determining the discharge characteristics of cutaneous mechanoreceptors. Raccoons, cats, and squirrel monkeys will be used to investigate the contributions and interactions of mechanical stimulus force and skin displacment as they affect the discharge of mechanoreceptive afferent fibers associated with the glabrous skin of a major tactile organ system, the forepaw, or hand. Single fibers of the median nerve will be isolated by microdissection in anesthetized subjects, and their peripheral receptive fields (RFs) will be subject to mechanical stimulation by a small probe. The probe is activated by a stimulating system which allows precise quantitative control of either skin displacement or applied force, and the simultaneous monitoring of both displacement and force, applied or reactive. Thus, in addition to examining the effects of various parameters of controlled displacement or force stimulation on mechanoreceptor discharge, it is also possible to monitor the effects of force on displacement and vica versa, thereby providing information regarding the role of viscoelastic properties of skin in determining mechanoreceptive afferent discharge. Absolute thresholds, adaptation, effects of stimulus magnitude, and trial-to-trial trends have been studied previously. Here, it is proposed to examine such variables as the role of stimulus diameter and shape, intertrial trends in discharge as a function of stimulus magnitude and duration when there is unsufficient time for full skin recovery between trials, effects of removal of all or part of the epidermal stratum corneum, effects of distance of stimulus from center of RF, and interactive effects of two stimuli applied in controlled spatial and temporal relationships. The proposed studies should further our understanding of the role of the integumental context of mechanoreceptors in determining their response to stimulation. This, in turn, should provide information relevant to the design and utilization of devices to aid in the use of touch as a substitute channel of communication by individuals handicapped in other sensory modalities.